1. Field of the Invention
The present invention relates to devices used to pull optical fiber cables through cable ducts, and more particularly, to such devices for use with optical fiber cables having more than one strength member.
2. Description of the Prior Art
The use of optical fibers is becoming prevalent in the telecommunications and data communications industries, and new building structures are being provided with cable ducts for the subsequent installation of optical fiber cables. Additionally, the telephone companies have found that the space in existing duct systems can be more effectively utilized by the use of optical fiber cable because of its small outer diameter, which is typically less than 0.90 inch.
A typical 4-inch duct has installed therein sub-ducts such as, for example, three 11/2-inch sub-ducts, or four 1-inch subducts, through which optical fiber cable is to be installed.
A typical optical fiber cable is formed about a central strength member which may be formed of either a single steel or a dielectric member or a plurality of twisted members. However, newer versions of optical fiber cables have multiple strength members running parallel to one another. Such multiple strength member cables are produced by a number of manufacturers including Alcatel Cable Systems and AT&T.
Due to the fragile nature of optical fibers, pulling cables through pre-installed ducts is a difficult and tedious task. Pulling eye assemblies were devised to facilitate the installation of cables through ducts. The pulling eyes provided a means for gripping the cable and, in particular, the strength components of the cable, so that stresses would not be exerted on the optical fibers while the cable was pulled through the duct system.
Due to the small size of the cable ducts, the cable diameter had to be maintained at a minimum, as did the diameter of the pulling eye assembly. Most existing pulling eyes have too large a diameter and therefore require larger duct sizes. In addition, the pulling eye had to be of such size that it could pass through bends having a predetermined minimum radius. A standard size requirement for pulling eyes is that a cable with an outer diameter of 0.7 inch must pass through a 1-inch sub-duct with a 24-inch bend radius.